1. Field of the Invention
The present invention relates to a catheter for injecting a therapeutic composition into a diseased part in a living body, particularly a cardiac ischemic part, or the surrounding portion thereof.
2. Description of the Related Art
The number of the patients of cardiac ischemic diseases has been increasing attendant on the increase of causes of danger, such as westernization of dietary life and the increase of social stresses. Particularly, the increase in the number of the patients of grave heart failure has come to be a serious problem in the developed countries; in the world, for example, no less than 15 million new patients have been generated yearly.
As a therapy for the cardiac ischemic diseases, gene therapy and cellular therapy have been being investigated. Conventional catheters applicable to such therapeutic approaches are provided at its distal end with an injection needle for injecting a therapeutic composition. For example, they are disclosed in U.S. Pat. No. 5,405,376 (corresponding to Japanese Unexamined Patent Publication No. Hei 8-508917) (Patent Reference 1), U.S. Pat. No. 5,797,870 (Patent Reference 2), U.S. Pat. No. 6,254,573 (Patent Reference 3), U.S. Pat. No. 6,309,370 (corresponding to Japanese Patent Laid-open No. 2001-87392) (Patent Reference 4), U.S. Pat. No. 5,972,013 (Patent Reference 5), U.S. Pat. No. 6,592,552 (corresponding to Japanese Unexamined Patent Publication No. 2001-516625) (Patent Reference 6), U.S. Pat. No. 5,931,810 (Patent Reference 7) and U.S. Pat. No. 6,102,887 (Patent Reference 8).
Specifically, Patent References 1 and 2 each disclose a catheter including a spirally formed injection needle. Patent References 3 and 4 each disclose a catheter including a contact-type sensor composed of a pressure sensor at a distal end portion thereof.
Patent References 5 and 6 each disclose a catheter including a mechanism for providing a negative pressure in the inside thereof so as to fix a distal end portion thereof to a tissue under suction. Patent Reference 7 discloses a puncture device for puncturing by mechanically gripping a tissue and fixing a distal end portion of the catheter to the tissue.
Patent Reference 8 discloses a catheter which includes an injection needle capable of being contained in a distal end portion thereof, and a fixing device to be opened radially outwards from the distal end portion. Incidentally, Patent Reference 8 discloses both a fixing device with sharp tips and a fixing device without sharp tips.
However, the catheters disclosed in the above patent references have the problems as follows. The spiral needle according to Patent References 1 and 2 has the merit that at the time of injecting a therapeutic composition into a tissue, the spiral needle does not slip off from the tissue and assured injection is possible, but the spiral needle has the demerit that it cannot be drawn out easily. Therefore, for example, in the condition where the spiral needle is puncturing a fragile myocardial infarction tissue, an erroneous movement of a distal end portion of the catheter may lead to the tear-off of the myocardial tissue by the spiral needle.
The contact-type sensor according to Patent References 3 and 4 is disposed at an end face of a distal end portion of the catheter and needs to be brought into assured contact with the myocardial tissue. Since the inside of a heart is highly rugged, however, the contact-type sensor is liable to generate errors and, therefore, is questionable about accuracy.
The catheter according to Patent References 5 and 6 is intended for use at a flat part which is not filled with a humor such as blood. Where the catheter is applied to a tissue surface which is filled with a humor and which is not necessarily flat, therefore, it is difficult to bring the distal end portion of the catheter into perfect contact with the tissue surface, and the catheter may suck the humor in.
The puncture device according to Patent Reference 7 is intended for gripping a comparatively strong heart. Therefore, where the puncture device is applied to a fragile tissue, for example, a myocardial infarction tissue, the puncture device may tear off the tissue.
The fixing device with sharp tips according to Patent Reference 8 makes it possible to fix the catheter to a tissue at the time of puncturing the tissue and injecting a therapeutic composition into the tissue. However, the fixing device is designed to be radially enveloped after puncturing the target tissue and, therefore, it is very high in invasiveness to the surrounding part of the target tissue. The fixing device without sharp tips according to Patent Reference 8 is designed for fixing the catheter to a tissue by spreading out trabeculae carneae in a heart. With the fixing device, therefore, it is very difficult to operate the catheter, and it is impossible to fix the catheter to an arbitrary part in the heart.